The invention relates to an injector for injection of at least one injection fluid and comprising a housing with a contact face for supporting on the skin, at least one chamber placed in the housing and containing an injection fluid, an injection needle which, in an activation direction intersecting both the at least one chamber and the contact face, is displaceably placed in the housing from a position of rest where the needle point is in front of the at least one chamberxe2x80x94seen in the activation directionxe2x80x94to an injection position where the point has penetrated the skin.
In recent years, allergies have become an increasing problem especially in the Western World. Therefore, the need for being able to diagnose such diseases quickly, securely and reproducibly is growing steadily.
Conventionally, allergies are diagnosed by manually putting a number of different allergen solutions on the palm side of the patient""s forearm. After this, an injection needle is pricked through the individual drops and about 1 mm into the skin so that a cavity is formed for absorbing some of the solution.
If the person is allergic to an allergen solution, the skin will after 10 to 15 minutes become red and swollen around the injection spot to an extent that depends on the quantity or the concentration of the solution that can be absorbed by the cavity. The degree of the allergic reaction can be given as a function of the extent of the swelling.
It is very difficult to dose the solution quantity with great accuracy, however, as the insertion depth of the needle and thereby the cubic capacity of the cavity depends solely on the operator""s routine and skill.
With the above conventional method, the degree of the allergic reaction can therefore not be estimated with the wanted accuracy and reproducibility.
As various allergen extracts are often used at tests of an allergic reaction, there is moreover an added risk of confusing the test solutions. Furthermore, the solutions are placed directly on the skin, which opens up the possibility of contamination with allergizing agents that might give a false positive response. By using this open handling of the allergen extracts, there is furthermore a risk of the operator becoming sensitized to one of the respective allergen extracts.
An additional problem of the conventional method is the risk of infection which is present to the operator in that the injection needle remains unprotected after use.
U.S. Pat. No. 5,099,857 discloses a construction with a movable injection needle and a sealed capsule containing an allergen solution. At injection, the needle will rupture the capsule, and the solution will therefore run out and form a drop on the skin, after which the needle via the drop will penetrate the skin in the same way as mentioned above. Also in this case, the estimate of the possible skin reaction will be inaccurate. Thus, there is a need for improvements in such devices.
The present invention provides an injector of the kind mentioned in the opening paragraph, whereby it is possible to perform an injection easily, quickly, and with greater accuracy and reproducibility than known so far.
At least one recess is made in the needle point for, by activating the injector, receiving a fixed quantity of injection fluid when the recess in the needle point is passing the at least one chamber. At least one membrane, which is firmly-connected to the housing, is placed after the at least one chamber.
Thereby, it is obtained that the dosing will be very accurate and that the depth of penetration of the needle can be fixed with great accuracy by means of an integrated stop so that e.g., the degree of an allergic reaction can be determined with wanted accuracy and uniformity.
At the point, the needle will inherently have a small extension transversely. The recess in the point can therefore advantageously be an eye which easily can be made with a sufficiently large volume and which is able to receive injection fluid from the two openings of the eye at the same time.
In the membrane, there can in advance be made a slot which at injection allows passage of the needle and during this fits tightly around the needle. When the needle point passes the chamber, injection fluid is accumulated in the recess and injection fluid is moreover deposited on the needle. The latter injection fluid is swept off the needle when this needle penetrates the tight-fitting slot so that there only remains the well-defined quantity of injection fluid in the recess of the needle. At the same time, the membrane serves for preventing any injection fluid in the punctured chamber from running out on the skin.
In an advantageous embodiment, the needle forms the slot whereby complete tightness and sterility of the housing interior in the position of rest of the injector before activation is ensured.
The housing can comprise a foot with the contact face and a top which carries the needle and is displaceably placed in relation to the foot so that the injector easily can be operated by a manual pressure on the top while the foot is supported on the skin.
In the foot, there can furthermore be made a through-going channel serving both for controlling the injection needle and accommodating the membrane and the chamber.
For accurate fixing of the penetration depth of the needle, there can, on the top and foot of the housing, be made a first and a second stop respectively that join in the injection position of the needle.
According to one embodiment of the invention, both foot and top can be made of a solid material. Between these two parts, there can furthermore be placed a compression spring for returning the needle completely or partly after injection so that the risk of accidents with the needle point is eliminated.
In a second embodiment of the invention, the top of the housing can be made of an elastomeric material and the top and the bottom can be firmly connected to each other. Thereby, it is possible to maintain a sterile environment in the injector. Furthermore, the air in the housing can advantageously be used as pressure means for returning the needle after injection.
In order to prevent that the injector is activated twice by accident, the housing can be completely or partly surrounded by an of a preferably thin material, such as paper. The envelope can be arranged to be deformed or broken when the injector is activated so that it can immediately be seen if the injector has been used. The envelope can advantageously also be used for, e.g., with a specific color, indicating the respective injection fluid in the injector.